The accurate characterization of submicrometer and nanometer sized particles presents a major challenge in the diverse applications envisaged for them including cosmetics, biosensors, renewable energy, and electronics. Size is one of the principal parameters for classifying particles and understanding their behavior, with other particle characteristics usually only quantifiable when size is accounted for. We present a comparative study of emerging and established techniques to size submicrometer particles, evaluating their sizing precision and relative resolution, and demonstrating the variety of physical principles upon which they are based, with the aim of developing a framework in which they can be compared. We used in-house synthesized Stöber silica particles between 100 and 400 nm in diameter as reference materials for this study. The emerging techniques of scanning ion occlusion sensing (SIOS), differential centrifugal sedimentation (DCS), and nanoparticle tracking analysis (NTA) were compared to the established techniques of transmission electron microscopy (TEM), scanning mobility particle sizing (SMPS), and dynamic light scattering (DLS). The size distributions were described using the mode, arithmetic mean, and standard deviation. Uncertainties associated with the six techniques were evaluated, including the statistical uncertainties in the mean sizes measured by the single-particle counting techniques. Q-Q plots were used to analyze the shapes of the size distributions. Through the use of complementary techniques for particle sizing, a more complete characterization of the particles was achieved, with additional information on their density and porosity attained.

No abstract

Respiration chambers are one of the primary sources of data on methane emissions from livestock. This paper describes the results from a coordinated set of chamber validation experiments which establishes the absolute accuracy of the methane emission rates measured by the chambers, and for the first time provides traceability to international standards, assesses the impact of both sensor and chamber response times on measurement uncertainty and establishes direct comparability between measurements made across different facilities with a wide range of chamber designs. As a result of the validation exercise the estimated T.D. Gardiner et al. 2absolute uncertainty associated with the overall capability across all facilities reduced from 25.7% (k=2, 95% confidence) before the validation to 2.1% (k=2, 95% confidence) afterwards.

New technology, the ultra stable low-noise current amplifier and the electron pump, provide new methods for making traceable measurements of small DC electric currents. We review four traceability routes for small current measurements and discuss the merits of each one. We present three case studies of small current calibrations, highlighting the role of noise and drifting instrument offsets. We show how the Allan deviation is used as a statistical tool for designing a calibration cycle to correctly eliminate drifting instrument offsets from calibration data. We also present a simplified noise model for a low-current ammeter which predicts a lower limit to the achievable statistical uncertainty in a calibration.

No abstract